The present invention relates to improvements to static high voltage switches and is advantageously applicable to the construction of a switchable high voltage generator.
It is known to use a bridge of electrically controlled switches based on semiconductor elements for opening a high voltage discharging circuit or closing a charging circuit, thus varying by a discreet value the level of the high voltage for the load circuit. The bridge is often formed by a plurality of series-connected thyristors, each having an avalanche diode connected in parallel and in the opposite direction for protection against overloads. The number of switch components to be placed in series is a function of the maximum voltage permitted by the component and the high voltage to be switched, as well as the cost and complexity of the control circuits. The latter comprise a transformer with a primary winding coupled to the same number of secondary windings as there are switches to be controlled. A construction of this type is inter alia described in U.S. Pat. No. 3,914,617.
This procedure has numerous disadvantages. More particularly in the case of miniaturized constructions the winding can be supported by a ferrite core, but it is difficult to obtain an adequate insulation and good coupling, the distribution of the fluxes cannot be balanced for all the secondary windings and the service life remains relatively limited.